In a weaving machine of this type, enabling, for example, the picking of two weft threads drawn respectively from two supply spools located on one side of the machine, the picking of the two weft threads is principally carried out by means of two picking nozzles supplied with compressed air and located on the side of the weaving machine. Each picking nozzle may be associated with a weft grip whose opening and closing action is itself controlled by pneumatic means.
The weft picking system also comprises, in general, other picking elements known as nozzle relays, or relay nozzles (i.e. auxiliary nozzles disposed along the picking axis), over the entire width of the weaving machine. These auxiliary nozzle relays which create air jets which complete the action of one or other of the picking nozzles in order to draw off and guide the weft threads until they reach the other side of the machine, are distributed in groups of N auxiliary nozzle, each group of auxiliary nozzle being supplied with compressed air via a pneumatic duct which is assigned thereto.
In accordance with the characteristics of the weft thread to be picked, it is necessary to adapt the picking parameters and, in particular, the compressed air pressures supplied to the various nozzles, as well as the operating times of these nozzles, so that the picking takes place, for each weft thread, under suitable conditions and without damaging the thread. Two or more compressed air pressures must therefore be available as well as two or more time sequences, and it must be possible to be able to select the pressure and sequence required for each weft thread as a function of the thread picking program carried out by the machine.